Method for improving the reactant gas flow in a reaction chamber

ABSTRACT

An epitaxial deposition method for processing a single wafer and a reaction chamber for conducting the method. The chamber has a substantially rectangular cross section reduced for increased system efficiency. Because the reduced cross section has insufficient room for a susceptor, the susceptor, in one embodiment, is mounted within a second portion of a dual height chamber having a greater cross sectional area. Purge gas supplied through an aperture in the chamber prevents undesirable deposits beneath the susceptor from reactant gas. The velocity profile and flow of reactant gas beneath the susceptor are controlled, for example, by a quartz plate which narrows and simultaneously shapes the gap between the susceptor and the input end of the chamber. Two types of reactant gas injectors can be used for controlling the velocity profile of injected gases.

This is a division of application Ser. No. 065,945, filed June 24, 1987,now U.S. Pat. No. 4,846,102.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to improved reaction chambersfor use in Chemical Vapor Deposition (CVD) systems, and moreparticularly to improvements in reaction chambers for use in epitaxialdeposition systems for processing wafers on a one-at-a-time basis andfor providing a more efficient deposition, a more uniform deposition onthe substrate or wafer to be processed, and for reducing or eliminatingdeposits beneath the susceptor.

2. Description of the Prior Art

Chemical Vapor Deposition (CVD) is the formation of a stable compound ona heated substrate by the thermal reaction or decomposition of certaingaseous compounds. Epitaxial growth is a highly specific type of CVDthat requires that the crystal structure of the substrate or wafer becontinued through the deposited layer.

Chemical Vapor Deposition systems take many forms but the basiccomponents of any CVD system usually include a reaction chamber whichhouses the wafer(s) to be processed, a gas control section, a timing andsequence control section, a heat source, and an effluent handlingcomponent. A great variety of ways of implementing each of thesecomponents leads to a great number of individual reactor configurationsin prior art systems.

The purpose of the reaction chamber is to provide a controlledenvironment for the safe deposition of stable compounds. The chamberboundary may be quartz, stainless steel, aluminum or even a blanket of anon-reacting gas, for example, nitrogen. Commercial epitaxial deposition(epi) reaction chambers are generally classified as being one of thefollowing three general types, depending primarily upon gas flow.Horizontal systems are employed wherein the wafers are placedhorizontally on a boat or susceptor and the gas flows horizontally inone end of the reaction chamber, across the wafers, and out the otherend. In vertical systems, the wafers are placed horizontally on asusceptor with the gas flow vertically toward the wafers from the topand the susceptor is normally rotated to provide more uniformtemperature and gas distributions. In cylindrical or barrel reactorsystems, the wafers are placed vertically on the outer surface of acylinder, and the gases flow vertically into the chamber from the topand pass over the wafers on the susceptor which rotates for uniformityof deposition.

Heating in a cold-wall CVD system is accomplished through the use ofradio frequency (RF) energy, or by radiation energy commonly in theultraviolet (UV), visible, or infrared (IR) bands or by resistanceheating. In an RF heated susceptor, the energy in an RF coil is coupledinto a silicon carbide coated carbon susceptor. The wafers are heatedthrough their contact with the susceptor. Radiant UV or IR heating isaccomplished by the use of high intensity lamps that emit strongly inthe ultraviolet, visible, and/or infrared spectrum. The large amounts ofenergy from these lamps heat the wafers and their holders by radiation.In both types of cold-wall heating, the walls of the chamber are cold,in comparison to the wafers themselves. The chamber walls must be cooledto prevent radiation from the lamps and the susceptor from producing alarge temperature rise.

The reaction chamber is used in epitaxial deposition systems to providethe carefully controlled environment needed for the epitaxial depositionto take place is a critical component of the epitaxial reactor. Threebasic reactor chamber configurations are used in the semiconductorprocessing industry including the horizontal reactor, the verticalreactor, and the barrel reactor, all of which where previously describedherein.

Prior to reactor heat-up, any residual air that remains in the chambermust be removed or purged. Prior to cool-down, following the depositioncycle, any gases remaining from the growth process are flushed out.

The various gases used in an epitaxial reaction chamber include anon-reactive "purge" gas which is used at the start and end of eachdeposition if the reaction chamber is opened to the atmosphere afterevery run as is normally done. The non-reactive purge gas, usuallynitrogen, is used to flush unwanted gases from the reaction chamber.

A carrier gas is used before, during, and after the actual growth cycle.The carrier gas is mixed with the gases responsible for etching, growth,or doping the silicon as each is added. Hydrogen is most often used as acarrier gas, although helium is sometimes employed.

Etching gases may be used prior to the actual epitaxial depositionwherein etching is performed to remove a thin layer of silicon from thesurface of the wafer together with any foreign matter or crystal damagethat is present on it. The etching prepares atomic sites for nucleatingor initiating the epitaxial deposition process.

The carrier gas is normally hydrogen. The source gases for siliconconventionally used for epitaxial depositions include Silane (SiH₄);Dichlorosilane (SiH₂ Cl₂); Trichlorosilane (SiHCl₃); and Silicontetrachloride (SiCl₄). The dopant gases normally used in epitaxialdeposition include Arsine (AsH₃); Phosphine (PH₃); and Diborane (B₂ H₆).The etching gas is commonly HCl.

The problems inherent in all prior art systems of Chemical VaporDeposition, and more particularly in the epitaxial deposition systems,include the non-uniform deposition on the surface of the wafer to beprocessed; the presence of contaminants in the reaction chamber prior toprocessing; wall deposits formed on the interior walls of the reactorchamber; deposition of the reactant chemicals on the heated susceptorand its support structure; inefficient gas flow characteristics; slowprocessing times; and non-uniform depositions due to uncontrolled gasvelocity profiles or gas density profiles.

These problems become even more inportant with the modern trend awayfrom batch processing systems toward single wafer orone-substrate-at-a-time processes. In a single wafer-at-a-timeprocessing system, the same volume of gas normally flowing through areaction chamber with many wafers to be processed cannot be used sincetoo much reactant gas will be consumed for one wafer. Still further, thecycle times to process a batch of wafers in a conventional batchprocessing system are far too long for single wafer processing. A singlewafer process requires a more rapid deposition rate to minimize thecycle time. Within a single wafer system, the deposits from reactionby-products build-up far more rapidly on a per wafer basis than in batchprocessing systems. Customers are increasingly demanding reducedparticulate contamination. As a result, these deposits must becontrolled or minimized in order to reduce the particulatecontamination.

These and other objects and advantages of the present invention will bemore fully understood after reading the Detailed Description of thePreferred Embodiments of the present invention, the Claims, and theDrawings which are briefly described hereinbelow.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved reactionchamber apparatus for use in CVD processing single substrates or waferson a one-at-a-time basis.

It is another object of the present invention to provide an improvedsingle wafer reaction chamber apparatus for use in epitaxial deposition.

It is yet another object of this invention to provide an improved singlewafer reaction chamber apparatus for use in a single wafer CVD systemwhich controls the reactant gas velocity profile to insure uniformdepositions.

It is a further object to provide an improved single wafer CVD reactionchamber for producing more uniform deposition than were heretoforepossible.

It is still a further object of this invention to provide an improvedsingle wafer CVD reaction chamber with a relatively fast processing timewithout wasting reactant gases.

It is yet a further object to provide an improved single wafer CVDreaction chamber which aids in substantially reduces deposits beneaththe susceptor.

It is still another object to provide an improved reaction chamberapparatus for use in a single wafer epitaxial deposition systemincluding a method and apparatus for increasing system efficiency byreducing carrier gas flow consumed on a per wafer basis.

The present invention provides an improved reaction chamber for us in aCVD system, and more particularly, for use in an improved single waferepitaxial deposition system for processing a single wafer-at-a-time withgreatly improved efficiency. The system of the present inventionincludes a reaction chamber having a top plate, a bottom plate parallelto the top plate, sides joining the top and bottom plate, a hollowinterior with a generally rectangular cross-section, a reactant gasinlet at one end of the hollow interior of the reaction chamber and agas outlet at the opposite end of the hollow interior of the reactionchamber for exhausting the at least partially spent gases therefrom.

In one embodiment of the improved epitaxial deposition reactor chamberof the present invention, an aperture is provided or formed in anintermediate portion of the bottom panel of the reaction chamber, and awell having a hollow interior cavity is connected with its open endcoterminous with the aperture and the remaining portion of the welldistending vertically downwardly therefrom. A susceptor support means ishoused at least partially within the well for positioning a susceptorfor demountably carrying or positioning a semiconductor wafer orsubstrate to be processed within the circular aperture in the bottompanel of the reaction chamber and either slightly above or slightlybelow the plane of the bottom panel, as desired. In this embodiment, theuse of the well for positioning the susceptor enables the height whichis measured as the vertical distance between the top panel and thebottom panel to be substantially reduced to approximately one half ofits normal height for providing a reduced cross-sectional area. Thereduced cross-sectional area of the hollow interior of the reactionchamber enables the velocity of the reactant gases, which are suppliedat a uniform flow rate, to be greatly increased and in fact doubled, soas to greatly reduce the processing time required for an epitaxialdeposition operation. Conversely, for a given flow rate, the reducedarea results in reduced total gas flow per unit time or per waferprocessed.

Normally, reducing the distance between the top and bottom panels isknown in the prior art to increase the undesirable wall depositsthereon. However, the present invention reduces the height whilesimultaneously reducing wall deposits downstream of the susceptorbetween the susceptor and the gas outlet end of the reaction chamber, ashereinafter described.

In an alternate embodiment of the epitaxial deposition reaction chamberof the present invention, a chamber is provided which has a first bottompanel disposed between the reactant gas input end of chamber and anintermediate portion of the hollow interior of the chamber. A secondsubstantially lower bottom panel is disposed between the intermediateportion of the chamber and the exhaust end thereof. An inwardly curvedvertical wall is used to interconnect the first bottom panel with thesecond or lower bottom panel to provide a dual height reaction chamber.The first height is significantly reduced between the top panel and thebottom panel for decreasing the cross-sectional area thereby greatlyincreasing the gas flow velocity of the reactant gas for reducing thetime required for the deposition operation and greatly reducing theamount of used gases. The lower portion of the chamber has a heightwhich is approximately twice the height of the input end of the chamber,so that it is able to house the susceptor and means for supporting thesusceptor within the chamber, and so that it provided ready access tothe susceptor and its support structure.

Each of the reaction chamber embodiments can include a quartz bib havingan inwardly curved end portion extending partially over the centralaperture or inwardly curved vertical wall to overhang the lower paneland at least partially encircle a portion of the circumference of thesusceptor for providing a narrow gap therebetween. The inwardly curvedportion can be shaped or sized to significantly narrow the gap at thecenter along the longitudinal axis of the reaction chamber to and widenthe gap in both directions toward the sides of the chamber for shapingthe velocity profile to a predetermined desired profile for optimizingthe uniformity of the deposition on the wafer.

Similarly, instead of quartz plate laying over the input end of thebottom panel, the bottom panel can be extended horizontally rearwardlyto provide the identical effect.

These and other objects and advantages of the present invention will bemore fully understood after reading the Detailed Description of thePreferred Embodiments of the present invention, the claims, and theDrawings which are briefly described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the preferred embodiment of theepitaxial deposition reaction chamber of the present invention;

FIG. 2 shows a partial perspective view of the epitaxial depositionreaction chamber of the embodiment of FIG. 3;

FIG. 3 illustrates a sectional side view of an alternate embodiment tothe epitaxial deposition reaction chamber of FIG. 3;

FIG. 4 is a partial perspective view of the embodiment of the epitaxialdeposition reaction chamber of FIG. 11;

FIG. 5 is a partial sectional side view of the input end of an epitaxialdeposition reaction chamber showing a quartz bib disposed on the bottompanel adjacent the outer periphery of the susceptor;

FIG. 6 is a blow-up of the circled portion of FIG. 5 showing the detailin the gap area;

FIG. 7 is a blow-up of the circled portion of FIG. 5 showing analternate embodiment to the quartz plate thereof;

FIG. 8 shows a top view of the susceptor, wafer, and quartz plate ofFIG. 5 illustrating the gap therebetween;

FIG. 9 is a partial sectional side view of the input end of the dualheight epitaxial deposition reaction chamber of FIGS. 3 and 4 showing aquartz plate therein;

FIG. 10 is a top view taken along view line 10--10 of FIG. 5 and showingthe relationship of the quartz plate to the susceptor;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a sectional side view of the preferred embodiment of theepitaxial deposition reaction chamber of the present invention which isreferred to herein as the "reduced area"; deep well" reaction chamber11. The reaction chamber 11 is shown as including a top panel 13 and abottom panel 15. Each of the panels 13 and 15 is an elongated, generallyrectangular, substantially planar quartz panel which is substantiallytransparent to visible and shorter wavelength radiation in apredetermined frequency range for producing a "cold-wall" reactor whileenabling the radiation to penetrate to the hollow interior 17 of thereaction chamber 11. The chamber 11 further includes a front end 19having a reactant gas input 21 and a rear end 23 having a spent gasoutput 25. The gas flow at the input end 19 of the reaction chamber 11is indicated by the gas flow direction arrow 27.

In an intermediate portion 29 of the hollow interior 17 of the reactionchamber 11, a circular aperture 31 is disposed in the lateral center ofthe bottom panel 15. A cylindrical well 33 operably distendssubstantially vertically downward from the bottom panel 15 at the outerperipheral edge of the circular aperture 31. The well 33 includescylindrical walls 35, a circular well bottom, floor or base 37, and ahollow interior or well cavity 36 formed interiorly of the cylindricalwalls 35 and the well bottom 37. A circular aperture or base aperture 39is formed in the center of the bottom 37 of the well 33. Positionedabove the center of the base aperture 39 within the top portion of thewell cavity 36 and at least partially within the circular base aperture31, a susceptor assembly 41 is housed. The assembly 41 includes asusceptor 43 having a planar top surface 55 for demountably positioningor carrying one substrate or wafer 45 to be processed. The susceptor 45may be supported by support apparatus including a pedestal 47, and ashaft 49 distending vertically downwardly from the center bottom portionof the pedestal 47. The shaft 49 passes through the center of the hollowcavity 36 of the well 33 and through the base aperture 39 for connectionto drive means positioned therebelow, as hereinafter described. A gasketor seal member may be positioned within the base aperture 39 about theshaft 49 for sealing purposes, and conventional bearings may also beused.

An annular gap 53 is formed within the outer peripheral portion of thecircular aperture 31 between the outer peripheral, rim, edge, orcircumference 59 of the susceptor 43 and the upper lip 55 of the well 33where the bottom plate 15 meets the vertically disposed cylindrical wellwall 35.

The reactant gases flow through the intermediate portion 29 of thereaction chamber 11 and a major portion of the reactant gas flow passesover the top surface of the wafer 45 to be processed while some portion(not shown) attempts to pass downwardly through the gap 53 and into thehollow interior 36 of the well 33 in the area beneath the susceptor 43.Any reactant gas passing through the annular gap 53 can form undesirablechemical coatings or deposits on the heated undersurface of thesusceptor 43 and its support structure 47, 49, the interior 36 of thewell 33, and the like, and these deposits may cause contaminationproblems, loss of time for cleaning, greatly reduced efficiency of thesystem, etc.

The vertical distance or height "d₁ " measured between the interiorsurface 63 of the top panel 13 and the interior surface 65 of the bottompanel 15 is approximately one half of the distance previously used inthe prior art systems. Reducing the height of at least the input portionof the reaction chamber 19 simultaneously reduces the cross-sectionalarea of the hollow interior 17 thereof.

The reduction of the height "d" to the distance "d₁ " would normallyprevent the reaction chamber 11 from being able to house the susceptorassembly as required therein. Therefore, the provision of the well 33provides the additional space required for housing the susceptor 43within the well 33 and at least partially within the circular aperture31 of the bottom panel 15 for positioning the susceptor 43 and the wafer45 demountably positioned thereon at least one of coplanar with theplane of the bottom surface 17 or slightly vertically disposed abovesaid plane, in order to obtain an optimal deposition on the wafer 45.The height or depth of the well 33 is given by "d₂ " and this dimensionis approximately equal to or slightly greater than the height "d₁ ".

The purpose of the reduced area input portions of the first embodimentof the reaction chamber 11 and the alternate embodiment of the reactionchamber 81 (as hereinafter described) is to reduce the gas flow requiredfor a given deposit. The embodiment of the reaction chamber 11 of FIG. 1reduces the gas flow required for a given deposition by a factor ofapproximately one half or more. Assuming the d₂ is slightly greater thand₁, even greater efficiencies can be realized. In order to control walldeposits in order to reduce the negative impact of the throughput byreducing the volume of the input area of the quartz tubes.

FIG. 2 shows a perspective view of the reaction chamber 11 of thepreferred embodiment of the present invention of FIG. 1. The reactionchamber 11 is shown as including a top panel 13 and a bottom panel 15. Apair of sides 71 are shown as interconnecting the edges of the top andbottom panels 13 and 15 to form an elongated, box-like constructionhaving a rectangular cross-section and a generally hollow interior. Thefront end 19 of the reaction chamber 11 is shown as including a flangeportion 77. The flange 77 is positioned adjacent a combination gate andreactant gas injector port 75, as hereinafter described. The opposite orrear end 23 of the reaction chamber 11 is shown as including a flange 73surrounding a spent gas outlet 22 for exhausting the at least partiallyspent gases from within the hollow interior of the chamber 17.

The reaction chamber 11 is shown as having a circular aperture 31disposed within an intermediate portion 29 of the floor 15 of thechamber 11, and a well 33 has its top opening coincident with theaperture 31. The well 33 has a generally cylindrical wall 35 dependingsubstantially vertically therefrom and extending downward to terminatein a circular well floor or base 37. The plane of the base 37 issubstantially parallel to the plane of the bottom panel 15, and theheight of the well "d₂ " is approximately equal to or slightly greaterthan the height of the chamber, measured as the perpendicular distancebetween the planes of the top panel 13 and the bottom panel 15. The base37 of the well 33 includes a central base aperture 39 which has,distending vertically downwardly therefrom, an elongated hollow tube 79having cylindrical walls 80, a hollow interior 83, and a purge gas inlet83.

FIG. 3 illustrates a second embodiment to the epitaxial depositionreaction chamber 11 previously described. In FIG. 3, the reactionchamber 81 is generally referred to as a "dual height" reaction chamber.The chamber 81 has a top panel 83 which is an elongated, generallyrectangular, substantially planar, quartz panel which is transparent tohigher frequency radiant energy so as to form a cold-wall reactor whosewalls are transparent to heat energy in a predetermined frequency rangeso that the walls remain cool while any absorbing material such as thesusceptor and wafer in the hollow interior 87 of the reaction chamber 81can be heated for facilitating the deposition reaction. The reactionchamber 81 also includes a first or front bottom panel 85 disposedbetween the front end 19 of the reaction chamber 81 and an intermediateportion 29 thereof. A vertical wall 87 depends substantially verticallydownward from the end of the first or front bottom panel 85 andterminates in a second or rear bottom panel 89 which is an elongated,generally rectangular, substantially planar, quartz panel.

A circular aperture 41 is formed in an intermediate portion 29 of thesecond bottom panel 89. A hollow tubular element 91 depends verticallydownward therefrom, and a shaft 49 depends vertically downward throughthe hollow interior 93 of the tube 91 along the longitudinal axisthereof. Purge gas is supplied to an inlet 95 in the tube 91 and thepurge gas is supplied to the hollow interior 93 bounded by tube walls 99of the tube 91 and then into the lower hollow interior portion 111 ofthe reactor 81 via the bottom circular aperture 41. The purge gas flowis shown by the purge gas flow direction arrows 97 and, the purge gasworks exactly the same as the purge gas usage previously described withreference to the preferred embodiment of the reaction chamber 61 of thepresent invention. The shaft 49 is shown as supporting the pedestal 47which in turn supports the susceptor 43 which demountably carries orpositions a wafer 45 thereon.

The front end 19 of the reaction chamber 81 of FIG. 3 is shown asincluding flange members 101 and a reactant gas injector port and gateassembly 103 is mounted in abutting relationship to the flange member101 for injecting reactant gases into the input 21 of the reactionchamber 81. Similarly, the rear 23 of the reaction chamber 81 includesflanges 105 and a spent gas output port and gate assembly 107 having aspent gas outlet 25. Furthermore, the beginning of the vertical wall 87at the junction of the first floor or bottom wall 85 is referred to asthe lip 109 and the area between the lip 109 and the outer peripheralcircumference, rim or edge 59 of the susceptor 45 defines a gap 110therebetween. The gap 110 connects the hollow interior 87 of the frontend 19 of the reaction chamber 81 with the hollow interior 111 beneaththe susceptor assembly 43 and the hollow interior 113 of theintermediate portion 29 and rear portion 23 of the reaction chamber 81.

FIG. 4 represents a perspective view of the dual height epitaxialdeposition reaction chamber 81 of the alternate embodiment of thepresent invention. In FIG. 4, the reaction chamber 81 is shown as havinga top panel 83, a first or front bottom panel 85 and a second or rearbottom panel 89. The vertical height between the top panel 83 and therear bottom panel 89 is approximately equal to or slightly greater thantwice the height of the input end of the reactor 81 measured as theperpendicular distance between the inside surface 115 of the top panel83 the inside surface 117 of the front bottom panel 85 of FIG. 3.

The front end 19 of the reaction chamber 87 is shown as terminating in aflange 101 positioned in a cooperating relationship with an input gateand reactant gas injector 103. The rear end 23 of the reaction chamber81 includes a flange 105 surrounding a gas outlet 25 for exhausting theat least partially expended, reacted, or spent reactant gases from thehollow interior 17 of the reaction chamber 81. The front bottom panel 85is shown as terminating in a curved vertical wall portion 35 whosebottom portion terminates the front end portion 19 and of the frontbottom panel 85. The height of the rear end portion of the reactionchamber 81, as measured between the inside surface 119 of the top paneland the inside surface 120 of its rear bottom panel 89 is equal to orslightly greater than twice the height of the front end portion 19 ofthe reactor 81 as measured between the inside surfaces 119, 120 of thetop 83 and the second lower panel 89.

An intermediate portion 29 of the rear bottom panel 89 includes acircular aperture 41 communicating with the top opening in a hollowcylindrical tube 91 distending vertically downwardly from the bottomsurface of the second bottom panel 89 and including a hollow interior 93surrounded by wall 99 and a purge gas inlet 95 disposed therein forsupplying purge gas to the hollow interior of the reaction chamber 81,as previously described.

FIG. 5 illustrates yet another embodiment of the improved epitaxialdeposition reaction chamber 11 of the present invention which includesfurther means for improving the deposition process while eliminating orat least significantly reducing undesirable chemical deposits beneaththe susceptor 43 and within the well 33, as previously described. InFIG. 5, the reduced area deep well reaction chamber 11 is shown aspreviously described in FIG. 1, and like reference numbers designatelike components, as known in the art, except that a bib or quartz plate121 is disposed with its bottom surface 118 on the interior surface 117of the bottom panel 15 between the front end 19 and the susceptor 43.The plate 121 is shown as including an extension portion 122 whichextends past or beyond the lip 61 of the well 33 so that the gap 53 ofFIGS. 1 and 2 is substantially reduced to a relatively narrower gap 125disposed between the rear edge or end portion 124 of the plate 121 andthe outer peripheral rim or circumference 59 of the susceptor 43. Thereduced area gap 125 further restricts the ability of the reactant gas27 to pass through the reduced area gap 125 and beneath the susceptor 43to form undesirable deposits thereon. The plate 121 is a separate pieceof quartz material and will be further described hereinafter.

FIG. 6 represents the dotted circle 91 of FIG. 5 and illustrates aportion of the apparatus of the system of FIG. 5 in greater detail. InFIG. 6, the flow arrow 27 illustrates that the reactant gas is passingover the wafer 47 and the bifurcated arrow 28 illustrates that a smallportion of the reactant gas is passing through the narrowed gap 125 intothe area 36 beneath the susceptor 43 and its support components. Thisreactant gas 28 causes undesirable deposits beneath the susceptor and onthe support components which can result in contamination of the wafer45. The quartz plate or bib 121 is shown as having its lower surface 118operatively supported on the upper interior surface 117 of the lowerwall 15. The wall 15 terminates in the vertical distending wall 35 ofthe well 33 and the area of intersection of the upper surface 117 of thelower wall 15 and the interior surface of the well wall 35 is referredto by the reference numeral 61 designating the lip of the well 33. Anextension portion or end portion 122 of the quartz plate 121 extendsbeyond the lip 61 and parallel to the inside surface of the floor 37 ofthe well 33 as previously described. The lower surface portion 124 ofthe extension portion 122 extends beyond the lip 61 and over the floor37 of the well 33 while the outer end portion 127 represents the rearend portion of the plate 121. The outer peripheral circumference or rim59 of the susceptor 43 is spaced a predetermined distance away from theouter end portion 124 of the plate 121 and a narrowed gap 125 existstherebetween. The gap 125 communicates with the hollow interior 36within the well 33 as previously described.

An alternate embodiment of the separate bib or quartz plate 81 is shownin FIG. 7. In FIG. 7, the individual plate 81 is replaced with anextension 129 of the bottom panel 15 of the reaction chamber 11. In FIG.7, the extension 129 is shown as overhanging the lip 61 of the wall 35of the well 33 since it extends radially inward over the entrance to thewell as defined by the circular aperture 31 in the base 15, so that thepoint where the bottom surface 15 meets the cylindrical wall 35 of thewell 33 is defined as the lip 61, and the extension or overhang 129passes horizontally outwardly thereover and terminates in the rear endportion 131 having the identical structure to the end portion 122 of theplate 81 previously described with reference to FIG. 7. The resultachieved by the embodiment of FIG. 7 is substantially identical to thatachieved with FIGS. 5 and 6, and the gap 125 is narrowed to the reducedarea gap 135 and shaped or dimensioned so as to have the narrowest gapportion 143 at the center and the widest gap portions 147 at the sidesfor reducing the chance of reactant gas flow into the area beneath thesusceptor as shown in FIG. 8. The reduced gap 135 is wider than reducedgap 125 to compensate for increased heating of the plate or bib 121 fromthe susceptor 45 in the area which is further downstream.

FIG. 8 shows a top view of the susceptor 45, wafer 47, and the bib orquartz plate 121 of FIG. 5. The plate 121 is shown as including arelatively straight front end 141 which is generally perpendicular tothe longitudinal axis 151 of the reactor 11, a pair of generallyparallel sides 137, 139 which are generally parallel to the longitudinalaxis 151 and to the sides of the reactor 11 and perpendicular to therear end 141, and a top planar surface 120. The sides 137, 139 arespaced a predetermined distance from the sides of the reactor chamber 11or in an abutting relationship thereto, as desired. The rear end 143 ofthe plate 121 is inwardly curved at the front end so as to provide arelatively narrow gap 145 between the outer peripheral edge of theinwardly-curved end portion 143 and the outer peripheral rim orcircumference 149 of the susceptor 43. The gap 145 between the inwardlycurved rear end portion 143 and the outer peripheral rim orcircumference 59 of the susceptor 43. The gap 145 between the inwardlycurved rear end portion 143 and the outer peripheral edge 59 of thesusceptor 43 which is at least partially encircled thereby isnon-linear. The inwardly curved end portion 143 is shaped or designed soas to produce a relatively narrow gap 145 at the center of the plate 121along the longitudinal axis 151 of the reaction chamber 11, and the gap145 widens as the inwardly curved surface 143 at the rear end extendslaterally outward from the longitudinal axis 151 towards the chambersides so that the gap continues to widen until it reaches a maximumwidth 147 between the outer longitudinal end portions of the sides 137,139 of the plate 121 and the outer peripheral rim 59 of the susceptor45.

As can be seen in FIG. 8, the rearwardly extending ends of the sides137, 139 forming the widest gap portions 147 and the wall 143 of therear end portion 143 at least partially encircle a portion of the outerperipheral circumference 59 of the susceptor 45, and in fact, encirclenearly 180° of the circumference 59. Therefore, the gap 145, 147 extendsalmost 180° about the outer peripheral rim 149 of the susceptor 45 andcontinually widens as it goes laterally from the narrowest center gapportion 145 toward the widest side gap portions 147 on opposite sides ofthe outer peripheral rim 149 of the susceptor 45. The narrowing of thegap 145 along the longitudinal center line or axis 151 of the reactor 45further reduces the chance of the reactant gas passing therethrough andforming undesirable deposits beneath the susceptor 45. Furthermore, thereduced area gap 145, 147 produces a positive effect on the reactant gasflow thereover. It serves to partially reshape the velocity profile ofthe gas passing thereover to insure the production of a more uniformdeposition on the surface of the wafer 47.

FIG. 9 illustrates a second embodiment to the epitaxial depositionreaction chamber 11 previously described. In FIG. 9, the reactionchamber 81 is generally referred to as a "dual height" reaction chamber.The chamber 81 has a top panel 83 which is an elongated, generallyrectangular, substantially planar, quartz panel which is transparent toultraviolet energy so as to form a cold-wall reactor whose walls aretransparent to heat energy in a predetermined frequency range so thatthe walls remain cool while the interior 87 of the reaction chamber 81is heated for facilitating the deposition reaction. The reaction chamber81 also includes a first or front bottom panel 85 disposed between thefront end 19 of the reaction chamber 81 and an intermediate portion 29thereof. A vertical wall 87 depends substantially vertically downwardfrom the end of the first or front bottom panel 85 and terminates in asecond or rear bottom panel 89 which is an elongated, generallyrectangular, substantially planar, quartz panel.

A circular aperture 41 is formed in an intermediate portion of thesecond bottom panel 89. A hollow tubular element 91 depends verticallydownward therefrom, and a shaft 49 depends vertically downward throughthe hollow interior 93 of the tube 91 along the longitudinal axisthereof. Purge gas is supplied to an inlet 95 in the tube 91 and thepurge gas is supplied to the hollow interior 111 of the lower portion ofthe reactor 81 via the bottom circular aperture 41. The purge gas flowis shown by the purge gas flow direction arrows 97 and, the purge gasworks exactly the same as the purge gas usage previously described withreference to the preferred embodiment of the reaction chamber 11 of thepresent invention. The shaft 49 is shown as supporting the pedestal 47which in turn supports the susceptor 43 which demountably carries orpositions the wafer 45 thereon. The bib or quartz panel 121 is shown asbeing disposed with its bottom surface 118 upon the interior topsurfaces 117 of the first bottom panel 85 and located between the frontend 19 and the susceptor 43. An extension portion 124 of the quartzplate 121 extends beyond the lip 61 of the junction of the intermediateend of the first lower panel 85 with the top of the vertical wall 88such that the horizontal extension 124 overhangs the second bottom panel89 and is substantially parallel thereto. This reduces or narrows thegap 125 between the curved rear end surface 127 of the plate 121 and aportion of the outer peripheral rim or circumference 59 of the susceptor43, as previously described it will be seen that the height "d₄ " of therear end portion 23 of the chamber 81 is substantially equal to twicethe verical height "d₃ " measured between the interior surface 115 ofthe top panel 83 and the interior surface 117 of the first bottom panel85 at the front end portion of the reactor 81. In addition to providingthe necessary space for mounting the susceptor 43 the wafer 45 pedestal47 and shaft 49, which could not otherwise be housed within the spacebetween the top panel 83 and the first bottom panel 85, the dual heightportion of the reaction chamber 81 at the rear end 23 provides adequateaccess space for installing the susceptor assembly and the plate 121, asdesired.

FIG. 10 shows a sectional top view of a portion of the reaction chamber81 of FIG. 9 illustrating the gap 125 between the inwardly curved endportion 127 of the plate extension 122 and the outer peripheral rim orcircumference 59 of the susceptor 45. The plate 121 is again shown ashaving a rear end 141 and a pair of parallel sides 137, 139 which aregenerally perpendicular to the front end 141 and generally adjacent tothe sides of the plate 121. The rear end portion 125 has an inwardlycurved surface 143 which defines a narrow gap 145 between the inwardlycurved surface 143 and the outer peripheral circumference 59 of thesusceptor 45. The gap 125 is shown as including a relatively narrowcenter portion 145 disposed along the longitudinal axis 151, and the gap145, 147 is shown as ever widening from the narrow central portion 145to the widest gap portion 147 at the opposite ends of the gap 147. Theinwardly curved surface 127 is shaped to provide this non-linear gap. Itwill be seen that a portion of the outer circumference 59 of thesusceptor 43 is encircled within the inwardly curved portion forming thegap 125. Some portion less than 180° of the circumference of thesusceptor 43 is so-encircled. The apparatus, instruction, operation andmethodology of the dual height epitaxial deposition reaction chamber 81of FIGS. 9 and 10 are substantially identical to that previouslydescribed, and will not be repeated herein. Anything previouslydescribed as an improvement on the reaction chamber 11 can be similarlyapplied to the reaction chamber 81 described herein.

As a parallel to the alternate embodiment of FIG. 10 to FIG. 9 acorresponding alternate embodiment exists to the structure of the dualheight reaction chamber 81 of FIGS. 9 and 10 and it is indicated by thedotted horizontal extension 181 of the first bottom wall 85 extendinghorizontally beyond the lip 61 of the vertical wall 88 into and over thesecond portion of the reaction chamber 81 and the bottom 89 thereof. Theextension 181 serves to replace the quartz plate 121, as previouslydescribed, and will not be further described herein.

In the preferred embodiment, the entire reaction chambers 11 and 81 havewalls 13, 15 and sides 65 made of quartz or any suitable material whichis transparent to the radiation used to heat the hollow interior of thereaction chamber 11, 81. Such chambers 11, 81 are typically referred toas "cold wall reactors". Typically, the material of the pedestal, thedistending shaft, the elongated hollow tubular element, and the bib orplate 121 is also fused quartz.

The wafers to be processes are typically silicon semiconductor wafers,since epitaxial deposition is the deposition of a single crystal layeron a substrate (often, but not always, of the same composition as thedeposited layer), such that the crystal structure of the layer is anextension of the crystal layer of the substrate. In this case, we canassume that a layer of silicon is being deposited into the surface ofthe silicon substrate or wafer to be processed.

the susceptor typically includes a graphite (carbon) body having a thincoating of silicon carbide over the outer surface thereof. The graphiteis "susceptible" to being heated. The "flush" gas used at the beginningand end of each deposition, is a non-reactive gas, such as hydrogen andsometimes nitrogen, which is used top flush away unwanted gases from thereaction chamber. Prior to the reactor heat up, any residual air thatmay inadvertently have entered the chamber is removed by the flushprocess. A carrier gas such as hydrogen is used in the preferredembodiment of the present invention, although hellum may also be used.The gases used in almost all epitaxial depositions of silicon arecompounds containing one silicon atom and four other atoms that areeither chlorine or hydrogen or a combination of the two. The four mostcommonly used sources of silicon include Silane (SiH₄); Dichlorosilane(SiH₂ Cl₂); Trichlorosilane (SiHCl₃) and Silicon Tetrachloride (SiCl₄).Similarly, the gases most commonly used to control the type ofconductivity and the resistivity of the epitaxial layer must becompatible with the gases already present in the reaction chamber. Theseare referred to as dopant gases and the most commonly used includeArsine (AsH₃); Phosphine PH₃); and Diborane (B₂ H₆).

It will be seen that in either the reduced area embodiment of thedeposition reaction chamber 11 or in the dual height reaction chamber81, that either the seperate quartz plate or bib can be used or ahorizontal extension of the lower wall at the input end of the reactionchamber to narrow the gap between the outer peripheral rim of thesusceptor and the inwardly curved end portion thereof.

Likewise, the system of the present invention can be used in anyconventional epitaxial deposition operation although it is preferablyused with the reaction chamber and susceptor positioning systemdisclosed and described in assignee's copending patent application, Ser.No. 032,474, filed on Mar. 31, 1987, and entitled ROTATABLE SUBSTRATESUPPORTING MECHANISM WITH TEMPERATURE SENSING DEVICE FOR USE IN CHEMICALVAPOR DEPOSITION EQUIPMENT, which is expressly incorporated by referenceherein.

It will be noted that in order to optimize the spacing between the levelof the susceptor with respect to the level of the bottom of the reactor,the shaft and pedestal supporting the susceptor can be selectivelyraised or lowered and finely tuned or adjusted for optimal performanceof the system. Furthermore, the shaft can be rotated to rotate thesusceptor and the wafer demountably carried thereon in order to averageout imperfections in the deposition process and provide a truly uniformdeposition on the surface of the wafer. In fact, the importance ofshaping the velocity profile of the incoming reactant gases lies in theface that the velocity profile produced can be shaped to produce eithera linear thickness distribution upstream-to-downstream or a trulyuniform coating on the surface of the wafer. If the wafer is rotated,the linear deposition will be averaged out and a truly uniformdeposition will result. Various features of the quartz plate, thenarrowed gap, and the like, further tend to produce or shape the desiredvelocity profile to optimize the uniformity of the deposition.

The narrowing of the cross-sectional area of the reaction chamber whichresults, serves to greatly increases the velocity of the gastherethrough, reducing processing time, reducing wasted gas, andreducing the amount of gas required for performing the depositionprocess so that the process becomes much more efficient, especially forprocessing a single wafer on a one-at-a-time basis, as comtemplated bythe system of the present invention.

It will be recognized, by those skilled in the art, that variousmodifications, variations, alterations, substitutions, and changes canbe made in the structure, components, materials, and the like set forthin the preferred embodiments described herein without departing from thespirit and scope of the present invention, which is limited only by theappended claims.

We claim:
 1. A method for processing a wafer within a reaction chamber,said method comprising in combination:a) receiving and exhausting areactant gas through an inlet and an outlet, respectively, of thereaction chamber, which reactions chamber includes a bottom panelextending downstream of the inlet and terminating at a terminal edge; b)supporting the wafer upon a susceptor assembly, which susceptor assemblyis downstream of the terminal edge of the bottom panel; c) locating thesusceptor assembly in a wall disposed proximate the terminal edge of thebottom panel to prevent the susceptor assembly from being in themainstream of reactant gas flow between the inlet and the outlet; and d)shaping the velocity profile of the flow of reactant gas flowing thesupported wafer to assist in carrying out the vapor deposition processmore uniformly across the wafer, said step of shaping including the stepof providing a varying flow rate of reactant gas through a gap, whichgap is defined between the terminal edge and the adjacent susceptorassembly perimeter, and into the well, the gap being of a predeterminedwidth at a central segment of the gap adjacent the susceptor assemblyperimeter upstream of the center of the susceptor assembly andincreasing in width in opposed directions along the terminal edge, thevarying reactant gas flow rate having a first value at the centralsegment of the gap and ranging along the gap in opposed directions to asecond value at the opposed extremities of the gap, whereby the velocityprofile of the reactant gas flow laterally across the wafer supported onthe susceptor assembly is a function of and modified by the reactant gasflow through the varying width gap upstream of the water.
 2. The methodfor processing a wafer within a reaction chamber as set forth in claim1, including the step of increasing the cross sectional area of thereaction chamber downstream of the susceptor assembly by a factor oftwo.
 3. The method for processing a wafer within a reaction chamber asset forth in claim 2 including the step of accessing the wafer from alocation downstream of the susceptor assembly.